Achieving the objectives of miniaturization and higher packing densities continue to drive the semiconductor manufacturing industry toward improving semiconductor processing in every aspect of the fabrication process. Several factors and variables are involved in the fabrication process. For example, at least one and typically more than one photolithography process may be employed during the fabrication of a semiconductor device. Each factor and variable implemented during fabrication must be considered and improved in order to achieve the higher packing densities and smaller, more precisely formed semiconductor structures.
In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the photoresist, and an exposing source (such as optical light, X-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the photoresist mask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Exposure of the coating through the photoresist mask causes a chemical transformation in the exposed areas of the coating thereby making the image area either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer. The resulting pattern image in the coating, or layer, may be at least one portion of a semiconductor device that contributes to the overall structure and function of the device.
Because the photoresist is used to form features on the semiconductor devices, the integrity of the photoresist must be maintained throughout the lithography process. That is, any flaw or structural defect which is present on a patterned photoresist may be indelibly transferred to underlying layers-during a subsequent etch process wherein the photoresist is employed.
An example of one type of photoresist is a chemically amplified resist (CAR). The CAR is a type of photoresist, typically used in deep ultraviolet (DUV) lithography, that relies on the catalytic action of a photo-generated acid during the post-exposure bake (PEB) process to alter the solubility of the exposed film. Since the acid catalyst is not consumed during PEB reaction, it can participate in multiple reaction cycles, thus providing an amplification mechanism.
However, environmental acid scavengers such as amine groups may be present in and/or around the processing chamber in which the CAR is processed and/or exposed. As a result, these acid scavengers may affect the acid catalyst concentrations thereby causing undesirable variations in the performance of the CAR.